Molecular weight regulates reversible adhesion of azopolymers with photoswitchable glass transition temperatures

Zhe Wang† ^b, Wen-Cong Xu†^c, Dachuan Zhang^b, Man Gao^d, Tao Chen^d, Youyi Sun*^a, Shuofeng Liang*^b and Si Wu*^b
aSchool of Materials Science and Engineering, North University of China, Taiyuan 030051, China. E-mail: syyi@pku.edu.cn
^bHefei National Research Center for Physical Sciences at the Microscale, Anhui Key Laboratory of Optoelectronic Science and Technology, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, China. E-mail: siwu@ustc.edu.cn; liangsf@ustc.edu.cn
^cShock and Vibration of Engineering Materials and Structures Key Laboratory of Sichuan Province, Mianyang, Sichuan 621999, China
^dGuangxi Proberoo Advanced Materials Co., Ltd, 41 Jianye Road, Liangqing District, Nanning 530221, China

First published on 13th August 2025

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Introduction

Advances in polymer science have revolutionized adhesive development by enabling precise control over material properties and multifunctionality.^1–4 While traditional high-strength adhesives offer robust bonding capabilities, their permanent nature limits their removability, whereas reusable adhesives frequently exhibit inadequate adhesion strength for specialized applications.⁵ In this context, stimuli-responsive reversible adhesives have emerged as a transformative solution, combining controlled detachment-reattachment cycles with on-demand functionality.^5–7 These systems are engineered through diverse stimuli-responsive mechanisms including thermal,^8–10 photo,^11–13 magnetic,^14,15 electrical,^16,17 and chemical triggers to address the limitations of conventional adhesive technologies.^18,19 Photoresponsive adhesives stand out for their superior spatiotemporal precision and exceptional tunability in both the intensity and wavelength of light activation.^5,20 Among these, azobenzene-based reversible adhesives have attracted considerable research interest due to their unique photoisomerization-driven adhesion properties.^21–28

Azobenzene is known for its ability to undergo reversible cis–trans photoisomerization, a property that can be harnessed in various applications.^29–34 Recent studies have demonstrated that certain azobenzene-containing polymers (azopolymers) and other photoresponsive polymers exhibit photoinduced reversible solid-to-liquid transitions, which are influenced by their photoswitchable glass transition temperature (T_g) values.^35–42 Trans azopolymers retain a solid-state with T_g values above room temperature, whereas cis azopolymers transition to a liquid state with T_g values below room temperature. This unique behavior positions azopolymers as promising candidates for reversible adhesives,^43–50 imprinting,^51–56 healable materials,^57–60 solar energy storage,⁶¹ and photomechanical applications.^62–65 Previous studies have shown that some monodisperse azopolymers exhibit photocontrolled reversible adhesion due to adhesion differences between their cis and trans isomers. However, regulating the sign (positive/negative) of this adhesion contrast remains a challenge, which is essential for developing and applying photoresponsive reversible adhesives. While molecular weight is a well-established determinant of adhesion strength in polymeric adhesives,^66,67 its regulatory effects on the reversibility and adhesion performance of azopolymers remain underexplored.

In this study, we synthesized a series of azopolymers with varying molecular weights through ring-opening metathesis polymerization (ROMP). Three distinct azopolymers P1, P2, and P3 were systematically investigated, with molecular weights strategically positioned below, near, and above the entanglement molecular weight (M_e). All these azopolymers exhibit photoswitchable T_gs and viscous flow temperatures (T_fs). Molecular weight emerged as a key determinant of photoresponsive behavior, with P3 exhibiting significantly elevated T_f values relative to those of P1 and P2. Furthermore, the molecular weight governed the photocontrolled adhesion performance: P1 functioned as a UV-weakened adhesive, P3 displayed UV-enhanced adhesion, and P2 remained largely unaffected by UV irradiation. These molecular-weight-dependent photoresponsive phenomena are rationalized by variations in polymer chain entanglement dynamics. Our findings highlight the critical role of molecular weight control in the design of effective reversible adhesives.

Results and discussion

We synthesized a monomer (MM) incorporating an n-butyl alkyl tail, an azobenzene moiety, a flexible spacer, and a polymerizable norbornene group via a multistep synthetic route (Fig. 1 and S1). The structure and intermediates of MM were characterized by ¹H NMR spectroscopy (Fig. S2–S4).

Azopolymers (P1, P2, and P3) with varying molecular weights were subsequently synthesized via ROMP (Fig. 1a). To regulate molecular weight, we systematically explored different polymerization conditions (Table 1) and evaluated the impact of catalysts G1, G2, H2, and G3 on the ROMP process. The number-average molecular weight (M_n), weight-average molecular weight (M_w), PDI, and conversion rates, were determined by GPC (Table 1).

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Among the tested catalysts, G3 achieved a higher conversion rate (95%), a narrow PDI (1.35), and an experimental M_n (75 kg mol⁻¹) close to the theoretical M_n (61 kg mol⁻¹) (Table 1, entry 4). In contrast, G1 and G2 exhibited broader PDIs, resulting in secondary metathesis reactions.⁶⁸ While H2 caused rapid gelation and the formation of insoluble solids within seconds (Table 1, entry 3 and Fig. S5). Based on these findings, G3 was selected for further experiments.

Since ROMP is governed by Gibbs free energy, the monomer concentration ([MM]) plays a crucial role in polymerization kinetics. We systematically investigated the effect of [MM] on ROMP (Table 1, entries 4–6). At lower concentrations, GPC traces exhibited acromion peaks, indicating intermolecular and intramolecular chain transfer reactions.⁶⁹ As [MM] increased to 0.4 mol L⁻¹, these acromion peaks completely disappeared, yielding an azopolymer with a narrow PDI (1.15) (Fig. S6).

The reaction kinetics of azopolymer synthesis via ROMP were analyzed. Real-time monitoring revealed a progressive decrease in the monomer concentration during polymerization, accompanied by a distinct shift of the polymer peak in GPC curves toward shorter elution times (Fig. 1b and S7), indicative of increasing molecular weight. Within the initial period, ln([M₀]/[M]) exhibited a linear relationship with time, confirming that ROMP follows first-order kinetics in this interval (Fig. S7). Between 3 and 5 minutes, molecular weight and PDI increased gradually. After 15 minutes, molecular weight plateaued, while PDI increased sharply, indicating the onset of chain transfer reactions. Based on these kinetics, 5 minutes was identified as the optimal reaction time, achieving a conversion rate of ∼90%, yielding an azopolymer with an M_n of 68 kg mol⁻¹ and a PDI of 1.13.

Under these optimized conditions, we synthesized azopolymers with varying molecular weights by adjusting the monomer/catalyst feed ratio (Table 1, entries 7–10). As the feed ratio increased, M_n increased linearly (Fig. 1c and d), closely matching theoretical predictions, with high conversion rates and low PDI values, confirming that the polymerization proceeded in a controlled manner.

To elucidate the molecular weight dependence of azopolymer properties, three distinct azopolymers P1, P2, and P3 with controlled molecular weights of 16 kg mol⁻¹, 68 kg mol⁻¹, and 233 kg mol⁻¹, respectively, were selected for comparative analysis (Table 1 and Fig. S8). M_e of the trans azopolymer was ∼38 kg mol⁻¹ (Fig. S10 and S11), estimated based on a reported method.⁷⁰ Thus, P1, P2, and P3 represent polymers with M_n values below, slightly above, and substantially above M_e, respectively.

The TGA curves revealed that all azopolymers decomposed at temperatures exceeding 300 °C, indicating high thermal stability of azopolymers (Fig. S12). SAXS, and WAXS data confirmed the formation of mesophases within the azopolymers (Fig. S13). Polarized optical microscopy (POM) images revealed small anisotropic grains dispersed within a largely isotropic matrix (Fig. S14), suggesting that the azopolymers exhibit characteristics of semicrystalline polymers, with both isotropic and anisotropic domains.

Tensile tests were performed to assess the effects of molecular weight on mechanical properties of azopolymers. P1 was brittle and could not form a free-standing specimen for test (Fig. 2a). In contrast, P2 formed stable, free-standing specimens, which exhibited an elongation at break of 11.69 ± 1.78% and a tensile strength of 15.11 ± 0.42 MPa (Fig. 2b). Notably, P3 demonstrated exceptional mechanical performance with a fracture elongation of 284.67 ± 5.39%, representing a 24-fold increase over P2, while retaining comparable tensile strength at 16.56 ± 0.44 MPa (Fig. 2c). This enhancement is attributed to M_n of P3 being significantly greater than that of M_e, leading to increased entanglements and elasticity.

Moreover, P3 exhibited excellent reprocessability due to its linear polymer chain structure. A P3 specimen was hot-pressed and reprocessed three times and retained consistent mechanical performance after each cycle (Fig. 2d–f), demonstrating its potential for sustainable applications.

The above results establish molecular weight as a critical determinant of the mechanical performance of azopolymers. Next, we examined its governing effects on photoresponsive behavior. Fig. 3a compares UV-vis absorption spectra of P1 in THF solution and annealed film states. The π–π* transition band displays a blue shift and broadening in the annealed film compared to solution, which is attributed to the aggregation and out-of-plane orientation of azobenzene chromophore.⁷¹

Azobenzene aggregates are typically classified as H-aggregates or J-aggregates, depending on the angle between coplanar transition dipoles and the interconnecting axis (Fig. 3b). To quantify these aggregates, we employed a Gaussian curve-fitting procedure on the absorption spectra, decomposing the contributions from H-aggregates, J-aggregates, and free azobenzene groups (Fig. 3c–e). In the azopolymer films of P1, P2 and P3, the estimated relative proportions were ∼55% H-aggregates, ∼40% free azobenzene groups, and ∼5% J-aggregates. Notably, molecular weight had minimal influence on aggregate proportions, suggesting that aggregation is governed primarily by chromophore interactions rather than polymer chain length effects.

The azopolymer films exhibit reversible cis–trans photoisomerization upon alternating UV and visible light irradiation (Fig. 4a). In the as-prepared state, azobenzene chromophores predominantly adopt the thermodynamically stable trans configuration.

Upon UV irradiation, the π–π* absorption band at ∼350 nm decreases, while the n–π* absorption band at ∼440 nm increases, indicating a trans-to-cis isomerization (Fig. 4b–d). Subsequent visible light irradiation restored the original π–π* absorption band at ∼350 nm and reduces the n–π* absorption at ∼440 nm, indicating cis-to-trans isomerization (Fig. 4b–d). The π–π* absorption band of trans azobenzene is at ∼350 nm and that of cis azobenzene is at ∼310 nm, the blue shift of absorption band after UV irradiation and red shift after visible light irradiation indicate cis–trans isomerization of azobenzene. The maximum absorbance of azopolymer increased after a cyclic irradiation because the stacking states and orientation of the azobenzene changed.^58,71 After UV and visible light irradiation, the estimated relative proportion of H-aggregates decreased, free azobenzene groups increased and J-aggregates remained roughly unchanged based on Gaussian curve-fitting procedure (Fig. 3, Fig. S15 and Table S1). Furthermore, the ratio of the absorbance of the π–π* band of trans-azobenzene groups (∼350 nm) to the φ–φ* band of phenyl groups (∼243 nm) serves as a useful parameter for determining azobenzene group orientation. Fig. 4b–d demonstrates that this ratio increases following UV and visible light irradiation, indicating that the azobenzene groups preferentially oriented perpendicular to the substrates prior to illumination.

These reversible spectral changes confirm that the azopolymers undergo repeatable cis–trans photoisomerization, demonstrating their potential for light-responsive applications (Fig. 4e–g).

Unlike previously reported azopolymers with similar structures,⁷² the azopolymers in this work exhibit photoinduced solid–liquid transition properties. We observed that trans-to-cis photoisomerization induced a solid-to-liquid transition of P1 (Fig. 5a). Upon UV irradiation (365 nm, 10.4 mW cm⁻²), the sharp edges of P1 powders gradually rounded, and some particles fused into droplets, indicating that photoinduced liquefaction occurred. In contrast, P2 and P3 powders exhibited negligible photoresponsive changes under UV irradiation (Fig. 5b and c). These results suggest that molecular weight plays a critical role in determining the photoinduced solid-to-liquid transition behavior of azopolymers.

To elucidate the effect of molecular weight on the photoinduced solid-to-liquid transition of azopolymers, we conducted DSC and temperature-dependent rheology tests on trans and cis P1, P2 and P3. During the DSC heating process, all three azopolymers exhibited a similar phase transition temperature (∼61 °C), corresponding to their isotropic transitions (Fig. 6a–c). Notably, no distinct T_g was observed for the trans azopolymers.

We further examine the thermal behavior of the cis-azopolymers, (Fig. 6d–f). The cis-content, determined via ¹H NMR integration, was 86%, 79%, and 90% for P1, P2 and P3, respectively (Fig. S9). In the first heating cycle, no clear T_g was detected, while an exothermic peak between 50 °C and 100 °C appeared, corresponding to the heat released during the cis-to-trans isomerization of azobenzene. During the subsequent heating cycle, the DSC curves of the cis azopolymers became identical to those of their trans counterparts, indicating complete thermal reversion of azobenzene to the trans form during the first heating cycle.

To further elucidate the effect of molecular weight on the thermal and viscoelastic properties of the azopolymers, we conducted temperature-dependent rheology tests on P1, P2, and P3 (Fig. 7).

In the temperature range of −10 °C to 60 °C, the storage moduli (G′) of the trans azopolymers remained around 2 × 10⁸ Pa, while their loss moduli (G′′) were approximately 1 × 10⁷ Pa, consistently lower than G′ (Fig. 7a–c). These results indicate that the azopolymers exhibited solid-like behavior within this temperature range. However, as the temperature increased to 60 °C, both G′ and G′′ dropped sharply. For P1 and P2, G′′ exceeded G′, marking the onset of viscous flow at 60 °C, in agreement with DSC data (Fig. 7a and b; Table 2).

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In contrast, P3 exhibited a distinct rubbery plateau between 60 °C and 114 °C, with G′ remaining higher than G′′ (Fig. 7c). This behavior suggests significant chain entanglement, which delays the transition to the viscous flow regime. Upon further heating to 114 °C, G′′ eventually surpassed G′, defining the T_f of P3 (Table 2). Additionally, changes in the slope of G′ were observed for all samples, corresponding to T_g (Table 2). These findings demonstrate that increasing molecular weight enhances entanglement effects, leading to increased polymer melt viscosity.

Upon UV irradiation, trans azopolymers were converted to their cis counterparts (Fig. S9). The cis azopolymers exhibited a lower T_g, ranging from −4 °C to −1 °C, indicating that azopolymers possess photoswitchable T_gs (Fig. 7d–f; Table 2). Notably, molecular weight significantly influenced T_fs of cis azopolymers. Cis P1 displayed no rubbery plateau above T_g, and a T_f value of −3 °C (Fig. 7d); Cis P2 exhibited comparable G′ and G′′ in the range of ∼20 °C −50 °C, suggesting a T_f value of 0 °C (Fig. 7e); Cis P3 demonstrated a broad rubbery plateau between ∼25 °C −93 °C, and a T_f value of 93 °C (Fig. 7f). The underlying mechanism of difference of photoswitchable T_fs is attributed to the molecular weight dependence of chain entanglement. Rheological measurements identified a M_e of 71 kg mol⁻¹ for cis azopolymers (Fig. S10). Progressive molecular weight increases intensify chain entanglement effects, driving systematic elevation of T_f. Notably, cis P3 achieves markedly higher T_f values than P1 and P2 due to its M_n significantly exceeding the M_e threshold.

Azopolymers have potential applications as photocontrolled adhesives. Azopolymer films were prepared by hot pressing at 100 °C, yielding uniform films with a thickness of 60 μm. The films were then cut into 5 mm × 5 mm pieces using a blade and sandwiched between two quartz slides, secured with clamps. The assembly was annealed at 80 °C for 2 hours, followed by cooling to room temperature to ensure strong adhesion, yielding the trans annealed samples, which were tested directly. For the cis samples, the trans samples were further irradiated at 365 nm (40.7 mW cm⁻²) for 10 minutes, followed by testing under light-protected conditions.

To investigate the effects of molecular weight on adhesion properties, we performed lap joint shear strength tests of trans P1, P2, and P3 at different temperatures (Fig. 8a). The adhesion strength of trans azopolymers increased with increasing molecular weight (Fig. 8b).

Specifically, for P1, P2, and P3, adhesion strength remained relatively stable between 25 °C and 50 °C but decreased significantly when the temperature increased to 70 °C (Fig. 8b–e). These results indicate that adhesion strength decreases sharply when the temperature exceeds the T_g of the azopolymer. However, this trend is partially mitigated by increasing molecular weight, as increased chain entanglement enhances adhesion retention at elevated temperatures.

Since molecular weight regulates the photoswitchable T_gs and T_fs of azopolymers, we hypothesized that it could also influence photocontrolled adhesion. At room temperature, the adhesion strengths of specimens bonded with trans P1, P2, and P3 were 1.19 ± 0.25, 2.06 ± 0.60, and 2.61 ± 0.25 MPa, respectively (Fig. 9a–c), indicating a positive correlation between adhesion strength and molecular weight. Upon UV irradiation, distinct adhesion responses were observed. The adhesion of the P1-bonded specimen decreased significantly to 0.20 ± 0.13 MPa, while that of P2 exhibited only a slight reduction (2.06 ± 0.60 to 1.73 ± 0.34 MPa). Notably, the P3-bonded specimen showed an increase in adhesion to 6.05 ± 1.23 MPa (Fig. 9f).

The observed changes in photocontrolled adhesion changes for P1, P2, and P3 arise from the interplay of two opposing factors: photoswitchable T_gs and T_fs reduce adhesion by softening the polymer matrix and trans-to-cis isomerization increases the dipole moment of azobenzene groups, enhancing polymer-substrate interactions.^5,24 To quantify the effect of dipole moments, theoretical calculations using the Gaussian 16 package were performed. The cis azopolymer units exhibited a dipole moment of 4.45 Debye, significantly greater than the 2.49 Debye of the trans form (Fig. 9d, e, and Fig. S16). As molecular weight increases, both the T_fs and viscosity values of cis azopolymers gradually rise. Consequently, cis P1 with lower molecular weights flow more readily. For P1, the photoswitchable T_gs and T_fs dominated, leading to a substantial loss of adhesion upon UV irradiation. Dipolar interactions cannot sustain strong adhesion of highly fluid cis P1, leading to adhesion failure. In contrast, cis P3 retained a viscoelastic character at room temperature, with a modulus two orders of magnitude higher than that of cis P1, making the photoswitchable T_gs and T_fs less effective in reducing adhesion. Instead, the increased dipole moment became the dominant factor. Conversely, the high viscosity of cis P3 restricts flow, enabling it to maintain robust adhesion strength through dipolar interactions. For P2, these opposing effects nearly cancel each other, resulting in minimal adhesion changes upon UV exposure.

As a result, P1 and P3 function as UV-weakened and UV- enhanced adhesives, respectively. A quartz-slide assembly bonded with P1 was able to hold a 2 kg dumbbell, but upon UV irradiation, the dumbbell dropped due to adhesion loss (Fig. 9g). Conversely, P3-bonded slides supported twice the initial load after UV irradiation, demonstrating significantly enhanced adhesion (Fig. 9h). The photocontrolled adhesion was highly stable, with five UV irradiation-thermal annealing cycles showing negligible performance degradation (Fig. 9i–k). These results highlight the ability to precisely tune azopolymer adhesion by adjusting molecular weight, enabling the design of both photo-weakened adhesives and photo-enhanced adhesives for diverse applications.

Conclusions

In conclusion, we synthesized azopolymers P1, P2, and P3 with molecular weights below, approaching, and exceeding M_e through ROMP. Increasing molecular weight was found to significantly enhance the mechanical properties of these azopolymers. All three polymers exhibited photoswitchable T_gs and T_fs. Notably, P3 demonstrated elevated T_f compared with P1 and P2, which was attributed to its more pronounced chain entanglement effect. When employed as photocontrolled adhesives, molecular weight-dependent photoinduced softening behavior led to contrasting effects: low-molecular-weight P1 showed UV-weakening characteristics, medium-molecular-weight P2 demonstrated negligible UV-induced changes, and high-molecular-weight P3 displayed UV-enhancing capabilities. Our findings demonstrate that molecular weight tuning enables precise customization of adhesive performance for diverse application scenarios. This work establishes molecular weight modulation as a versatile design strategy for developing smart switchable adhesives.

Materials and methods

Materials

cis-5-Norbornene-exo-2,3-dicarboxylic anhydride (>99%) and Grubbs second-generation catalyst (G2) (>98%) were purchased from Aladdin. 6-Aminohexanoic acid (>98%), 6-chlorohexanol (>95%), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI) (>99%), N,N-diisopropylethylamine (DIPEA) (>99%), and 4-dimethylaminopyridine (DMAP) (>99%) were purchased from Macklin. 4-(4-Butylphenylazo)phenol (>98%) was purchased from TCI. Anhydrous grade dichloromethane (DCM) (>99.9%, water <30 ppm) was purchased from Energy Chemical and used as the solvent for polymerization. All the other solvents were purchased from Sinopharm. Grubbs third-generation catalyst (G3) was synthesized according to the literature.⁷³

Methods

The synthesis and characterization procedures for the azopolymers (P1, P2 and P3) are detailed in the SI. Ultraviolet–visible (UV-vis) absorption spectra were recorded using a UV-2600 spectrometer. The molecular weights and polydispersity indices (PDIs) of the azopolymers were determined by gel permeation chromatography (GPC) using a 1260 Infinity system with a refractive index detector at 35 °C. THF was used as the eluent at a flow rate of 0.5 mL min⁻¹, and polystyrene standards were used for calibration. Differential scanning calorimetry (DSC) measurements were conducted using a DSC 3 system under a nitrogen atmosphere, with temperatures ranging from −50 to 150 °C and heating/cooling rates of 10 °C min⁻¹. Thermogravimetric analysis (TGA) was performed on a DTG-60 system at a heating rate of 10 °C min⁻¹, also under nitrogen. Rheological measurements were executed with an HR20 rheometer, applying shear deformation within the linear viscoelastic response range of the samples, using plate-plate geometry with 8 mm diameter plates. The temperature-dependent experiments were conducted under a nitrogen atmosphere, with a heating rate of 3 °C min⁻¹ and a constant angular frequency of 10 rad per s. The frequency-dependent experiments were conducted under a nitrogen atmosphere, with angular frequencies ranging from 0.1 to 100 rad per s. ¹H nuclear magnetic resonance (¹H NMR) spectra were obtained using a 400 MHz spectrometer at 25 °C. Stress–strain curves and lap joint shear strength tests were performed with a SUNS UTM4303 electronic universal testing machine. Small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) analyses were carried out using a SAXSpoint 2.0 system. The trans-to-cis photoisomerization of the azopolymers was induced using a light-emitting diode (LED) at 365 nm, while cis-to-trans isomerization was achieved with an LED at 530 nm. The output power of the LEDs was regulated using an LED controller. Optical microscopy images were captured with an optical microscope equipped with a charge-coupled device (CCD) camera.

Author contributions

S. W. led the project. S. W., W.-C. X. and Z. W. conceived the idea. W.-C. X., Z. W., Y. S., S. L. and S. W. designed the experiments. Z. W., W.-C. X., D. Z., M. G., T. C., Y. S., S. L. and S. W. performed the experiments and analysed the data. S. W., Y. S., S. L., W.-C. X. and Z. W. wrote the manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the SI. The SI includes NMR, GPC, rheology, TGA, SAXS, and WAXS characterization data for this article. See DOI: https://doi.org/10.1039/d5py00606f.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (NSFC, No. 22405256, 52120105004, 52425302 and 52350233), Fundamental Research Funds for the Central Universities (WK3450000006 and WK2060190102), Anhui Provincial Natural Science Foundation (No. 1908085MB38), and Hefei Municipal Natural Science Foundation (No. 2021013). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. This work was partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication, and the Instruments Center for Physical Science, University of Science and Technology of China.

References

1. M. Li, A. Mao, Q. Guan and E. Saiz, Chem. Soc. Rev., 2024, 53, 8240–8305 RSC .
2. D. Hwang, C. Lee, X. Yang, J. M. Perez-Gonzalez, J. Finnegan, B. Lee, E. J. Markvicka, R. Long and M. D. Bartlett, Nat. Mater., 2023, 22, 1030–1038 CrossRef .
3. S. Pal, J. Shin, K. DeFrates, M. Arslan, K. Dale, H. Chen, D. Ramirez and P. B. Messersmith, Science, 2024, 385, 877–883 CrossRef PubMed .
4. Z. Zhang, E. C. Quinn, J. K. Kenny, A. Grigoropoulos, J. S. DesVeaux, T. Chen, L. Zhou, T. Xu, G. T. Beckham and E. Y. X. Chen, Science, 2025, 387, 297–303 CrossRef .
5. Y. L. Tan, Y. J. Wong, N. W. X. Ong, Y. Leow, J. H. M. Wong, Y. J. Boo, R. Goh and X. J. Loh, ACS Nano, 2024, 18, 24682–24704 CrossRef .
6. Z. Liu and F. Yan, Adv. Sci., 2022, 9, 2200264 CrossRef .
7. M. Kim, H. Lee, M. C. Krecker, D. Bukharina, D. Nepal, T. J. Bunning and V. V. Tsukruk, Adv. Mater., 2021, 33, 2103674 CrossRef PubMed .
8. H. Lee, D. S. Um, Y. Lee, S. Lim, H. j. Kim and H. Ko, Adv. Mater., 2016, 28, 7457–7465 CrossRef PubMed .
9. Z. Wang, K. Huang, X. Wan, M. Liu, Y. Chen, X. Shi and S. Wang, Angew. Chem., Int. Ed., 2022, 61, e202211495 CrossRef PubMed .
10. F. Yang, A. Cholewinski, L. Yu, G. Rivers and B. Zhao, Nat. Mater., 2019, 18, 874–882 CrossRef CAS PubMed .
11. T.-Y. Xu, M. Cui, C. Zhao, S.-W. Zhou, T.-L. Zhang, H.-Y. Lin, F. Tong and D.-H. Qu, CCS Chem., 2024, 6, 1071–1084 Search PubMed .
12. J. Liu, Y.-S. Huang, Y. Liu, D. Zhang, K. Koynov, H.-J. Butt and S. Wu, Nat. Chem., 2024, 16, 1024–1033 CrossRef CAS PubMed .
13. E. Kizilkan, J. Strueben, A. Staubitz and S. N. Gorb, Sci. Robot., 2017, 2, eaak9454 CrossRef PubMed .
14. S. Wang, H. Luo, C. Linghu and J. Song, Adv. Funct. Mater., 2021, 31, 2009217 CrossRef CAS .
15. W. Wang, J. V. I. Timonen, A. Carlson, D.-M. Drotlef, C. T. Zhang, S. Kolle, A. Grinthal, T.-S. Wong, B. Hatton, S. H. Kang, S. Kennedy, J. Chi, R. T. Blough, M. Sitti, L. Mahadevan and J. Aizenberg, Nature, 2018, 559, 77–82 CrossRef CAS PubMed .
16. J. Shintake, S. Rosset, B. Schubert, D. Floreano and H. Shea, Adv. Mater., 2015, 28, 231–238 Search PubMed .
17. L. K. Borden, A. Gargava and S. R. Raghavan, Nat. Commun., 2021, 12, 4419 CrossRef CAS PubMed .
18. W. Li, X. Liu, Z. Deng, Y. Chen, Q. Yu, W. Tang, T. L. Sun, Y. S. Zhang and K. Yue, Adv. Mater., 2019, 31, 1904732 CrossRef CAS .
19. S. Arias, S. Amini, J. Horsch, M. Pretzler, A. Rompel, I. Melnyk, D. Sychev, A. Fery and H. G. Börner, Angew. Chem., Int. Ed., 2020, 59, 18495–18499 Search PubMed .
20. G. Xu, S. Li, C. Liu and S. Wu, Chem. – Asian J., 2020, 15, 547–554 Search PubMed .
21. Z. Wu, C. Ji, X. Zhao, Y. Han, K. Müllen, K. Pan and M. Yin, J. Am. Chem. Soc., 2019, 141, 7385–7390 CrossRef CAS PubMed .
22. X. Huang, Z. Shangguan, Z.-Y. Zhang, C. Yu, Y. He, D. Fang, W. Sun, Y.-C. Li, C. Yuan, S. Wu and T. Li, Chem. Mater., 2022, 34, 2636–2644 Search PubMed .
23. P. Zhang, F. Cai, W. Wang, G. Wang and H. Yu, ACS Appl. Polym. Mater., 2021, 3, 2325–2329 CrossRef CAS .
24. T.-H. Lee, G.-Y. Han, M.-B. Yi, H.-J. Kim, J.-H. Lee and S. Kim, ACS Appl. Mater. Interfaces, 2021, 13, 43364–43373 Search PubMed .
25. M. Koike, M. Aizawa, H. Minamikawa, A. Shishido and T. Yamamoto, ACS Appl. Mater. Interfaces, 2021, 13, 39949–39956 CrossRef CAS PubMed .
26. L. Kortekaas, J. Simke, D. W. Kurka and B. J. Ravoo, ACS Appl. Mater. Interfaces, 2020, 12, 32054–32060 CrossRef CAS PubMed .
27. Z. Lin, J. Feng, L. Fang, Y. Zhang, Q. Ran, Q. Zhu and D. Yu, Adv. Mater., 2024, 36, 240645 Search PubMed .
28. S. Ito, H. Akiyama, M. Mori, M. Yoshida and H. Kihara, J. Polym Sci., 2020, 58, 568–577 CrossRef CAS .
29. H. M. D. Bandara and S. C. Burdette, Chem. Soc. Rev., 2012, 41, 1809–1825 RSC .
30. N. Anwar, T. Willms, B. Grimme and A. J. C. Kuehne, ACS Macro Lett., 2013, 2, 766–769 CrossRef CAS .
31. Y. Norikane, E. Uchida, S. Tanaka, K. Fujiwara, E. Koyama, R. Azumi, H. Akiyama, H. Kihara and M. Yoshida, Org. Lett., 2014, 16, 5012–5015 CrossRef CAS PubMed .
32. E. Uchida, R. Azumi and Y. Norikane, Nat. Commun., 2015, 6, 7310 Search PubMed .
33. T. Dang, Z.-Y. Zhang and T. Li, J. Am. Chem. Soc., 2024, 146, 19609–19620 Search PubMed .
34. S. Sun, S. Liang, W.-C. Xu, G. Xu and S. Wu, Polym. Chem., 2019, 10, 4389–4401 RSC .
35. H. Zhou, C. Xue, P. Weis, Y. Suzuki, S. Huang, K. Koynov, G. K. Auernhammer, R. Berger, H.-J. Butt and S. Wu, Nat. Chem., 2017, 9, 145–151 CrossRef CAS .
36. W. C. Xu, S. Sun and S. Wu, Angew. Chem., Int. Ed., 2019, 58, 9712–9740 CrossRef CAS PubMed .
37. R. H. Zha, G. Vantomme, J. A. Berrocal, R. Gosens, B. de Waal, S. Meskers and E. W. Meijer, Adv. Funct. Mater., 2017, 28, 1703952 CrossRef .
38. J. Li, M. W. Wang, Y. Liu, W. M. Ren and X. B. Lu, Angew. Chem., Int. Ed., 2021, 60, 17898–17903 Search PubMed .
39. C. Lee, D. Ndaya, R. Bosire, N. K. Kim, R. M. Kasi and C. O. Osuji, J. Am. Chem. Soc., 2021, 144, 390–399 Search PubMed .
40. S. Yang, J. D. Harris, A. Lambai, L. L. Jeliazkov, G. Mohanty, H. Zeng, A. Priimagi and I. Aprahamian, J. Am. Chem. Soc., 2021, 143, 16348–16353 CrossRef CAS .
41. C. Shang, Z. Xiong, S. Liu and W. Yu, Macromolecules, 2022, 55, 3711–3722 CrossRef CAS .
42. S. Sun, C. Yuan, Z. Xie, W.-C. Xu, Q. Zhang and S. Wu, Polym. Chem., 2022, 13, 411–419 Search PubMed .
43. S. Ito, H. Akiyama, R. Sekizawa, M. Mori, M. Yoshida and H. Kihara, ACS Appl. Mater. Interfaces, 2018, 10, 32649–32658 CrossRef CAS PubMed .
44. R. Zhao, J. Mu, J. Bai, W. Zhao, P. Gong, L. Chen, N. Zhang, X. Shang, F. Liu and S. Yan, ACS Appl. Mater. Interfaces, 2022, 14, 16678–16686 CrossRef CAS .
45. Y. Zhou, M. Chen, Q. Ban, Z. Zhang, S. Shuang, K. Koynov, H.-J. Butt, J. Kong and S. Wu, ACS Macro Lett., 2019, 8, 968–972 CrossRef CAS .
46. J. J. B. van der Tol, T. A. P. Engels, R. Cardinaels, G. Vantomme, E. W. Meijer and F. Eisenreich, Adv. Funct. Mater., 2023, 33, 2301246 CrossRef CAS .
47. J. Li, Q. Y. Zhang and X. B. Lu, Angew. Chem., Int. Ed., 2023, 62, e202311158 CrossRef CAS .
48. H. Akiyama, T. Fukata, A. Yamashita, M. Yoshida and H. Kihara, J. Adhes., 2016, 93, 823–830 CrossRef .
49. S. Ito, A. Yamashita, H. Akiyama, H. Kihara and M. Yoshida, Macromolecules, 2018, 51, 3243–3253 Search PubMed .
50. Y. Feng, J. Wei, L. Qin and Y. Yu, Soft Matter, 2023, 19, 999–1007 RSC .
51. S. Liang, C. Yuan, C. Nie, Y. Liu, D. Zhang, W. C. Xu, C. Liu, G. Xu and S. Wu, Adv. Mater., 2024, 36, e2408159 CrossRef .
52. Y. Liu, S. Liang, C. Yuan, A. Best, M. Kappl, K. Koynov, H.-J. Butt and S. Wu, Adv. Funct. Mater., 2021, 31, 2103908 CrossRef CAS .
53. W. C. Xu, C. Liu, S. Liang, D. Zhang, Y. Liu and S. Wu, Adv. Mater., 2022, 34, 2202150 CrossRef CAS .
54. B. Yang, F. Cai, S. Huang and H. Yu, Angew. Chem., Int. Ed., 2020, 59, 4035–4042 CrossRef CAS PubMed .
55. K.-T. Lin, Y.-J. Chen, M.-R. Huang, V. K. Karapala, J.-H. Ho and J.-T. Chen, Nano Lett., 2020, 20, 5853–5859 Search PubMed .
56. C. Liu, A. K. Steppert, Y. Liu, P. Weis, J. Hu, C. Nie, W. C. Xu, A. J. C. Kuehne and S. Wu, Adv. Mater., 2023, 35, 2303120 CrossRef CAS PubMed .
57. H. I. Jeon, S. Jo, S. Jeon, T. Jun, J. Moon, J. H. Cho, H. Ahn, S. Lee, D. Y. Ryu and T. P. Russell, ACS Nano, 2023, 17, 8367–8375 CrossRef PubMed .
58. S. Liang, S. Li, C. Yuan, D. Zhang, J. Chen and S. Wu, Macromolecules, 2023, 56, 448–456 Search PubMed .
59. D. Shen, Y. Yao, Q. Zhuang and S. Lin, Macromolecules, 2021, 54, 10040–10048 CrossRef .
60. Z. Zhang, M. Chen, I. Schneider, Y. Liu, S. Liang, S. Sun, K. Koynov, H.-J. Butt and S. Wu, Macromolecules, 2020, 53, 8562–8569 CrossRef .
61. X. Xu, P. Zhang, B. Wu, Y. Xing, K. Shi, W. Fang, H. Yu and G. Wang, ACS Appl. Mater. Interfaces, 2020, 12, 50135–50142 Search PubMed .
62. A. S. Kuenstler, K. D. Clark, J. Read de Alaniz and R. C. Hayward, ACS Macro Lett., 2020, 9, 902–909 Search PubMed .
63. M. Chen, B. Yao, M. Kappl, S. Liu, J. Yuan, R. Berger, F. Zhang, H. J. Butt, Y. Liu and S. Wu, Adv. Funct. Mater., 2019, 30, 1906752 Search PubMed .
64. H. Zhou, A. S. Kuenstler, W. Xu, M. Hu and R. C. Hayward, Macromolecules, 2022, 55, 10330–10340 Search PubMed .
65. F. Cai, B. Yang, X. Lv, W. Feng and H. Yu, Sci. Adv., 2022, 8, eabo1626 Search PubMed .
66. W. Qiu, Y. Huang, H. Zhu, Y. Long, Q. Zhang and S. Zhu, Chem. Eng. J., 2024, 496, 153880 Search PubMed .
67. B. T. Poh and A. T. Yong, J. Adhes., 2009, 85, 435–446 Search PubMed .
68. C. W. Bielawski, D. Benitez, T. Morita and R. H. Grubbs, Macromolecules, 2001, 34, 8610–8618 CrossRef .
69. C. W. Bielawski and R. H. Grubbs, Prog. Polym. Sci., 2007, 32, 1–29 CrossRef .
70. C. Liu, J. He, E. v. Ruymbeke, R. Keunings and C. Bailly, Polymer, 2006, 47, 4461–4479 CrossRef .
71. X. Tong, L. Cui and Y. Zhao, Macromolecules, 2004, 37, 3101–3112 CrossRef .
72. J. Chen, T. Xu, W. Zhao, L.-L. Ma, D. Chen and Y.-Q. Lu, Polymer, 2021, 218, 123492 CrossRef .
73. J. A. Love, J. P. Morgan, T. M. Trnka and R. H. Grubbs, Angew. Chem., Int. Ed., 2002, 41, 4035–4037 CrossRef PubMed .

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Footnote

† These authors contributed equally to this work.

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